Magnetic and EMR signatures of metal-support interaction in Pd/CeO2/C electrocatalysts for formate electrooxidation reaction

This study investigates how CeO 2 nanoparticle morphology modulates electronic structure, magnetic behavior, and interfacial chemistry, and how these properties relate to formate electrooxidation over Pd. Two morphologies are compared: hydrothermally synthesized CeO 2 nanocubes (CeO 2 NC) and commercial CeO 2 polyhedra (CeO 2 poly). Pd nanoparticles supported on carbon (Pd/C) and on ceria-carbon composites (Pd/CeO 2 /C NC and Pd/CeO 2 /C poly) are prepared by NaBH 4 reduction. X-ray diffraction (XRD) reveals morphology-dependent microstrain in CeO 2 . Transmission Electron Microscopy (TEM) confirms CeO 2 NC (∼30 nm), CeO 2 poly (∼50 nm), and Pd NPs (4-10 nm). Energy-Dispersive X-ray Spectroscopy (EDS) mapping shows co-localization of Pd and Ce. X-ray Photoelectron Spectroscopy (XPS) indicates higher Ce 3+ and oxygen vacancy concentrations for CeO 2 NC, and increased Pd 0 (∼20%) compared to Pd/C. Magnetic measurements show Pd/CeO 2 /C NC has 23-24 times lower saturation magnetization (M s ) than Pd/C, while Pd/CeO 2 /C poly exhibits Ms similar to Pd/C. Electron Magnetic Resonance (EMR) analysis reveals three contributions: a ferromagnetic Pd-ceria component, a paramagnetic carbon signal near Pd/ceria, and a paramagnetic Pd-carbon interaction. Electrochemical tests demonstrate a clear morphology effect, with Pd/CeO 2 /C NC showing the most negative onset potential (−0.47 V), the highest peak current (1.57× Pd/C), and superior chronoamperometric stability.